1. Field of the invention
The present invention relates to a silica based glass waveguide and an optical module using the same, and more specifically to a silica based glass waveguide and an optical module using the same for use in large-capacity optical transmission system.
2. Prior Art
Recently, accompanied with propagation of technology such as internet and high speed communication between computers, developments and improvements of long distance high speed large-capacity transmission system using dense wavelength division multiplexing (DWDM) method are advancing rapidly in the worldwide scale.
In DWDM transmission system, large capacity transmission is performed by multiplexing different wavelength optical signals of 1.55 μm band width to an optical fiber by using an optical multiplexer/demultiplexer, then amplify this multiplexed optical signal collectively with an optical fiber amplifier. As a key component of this DWDM transmission system, an optical multiplexer/demultiplexer which multiplexes or demultiplexes different wavelength optical signals is indispensable.
As an optical multiplexer/demultiplexer, three types of dielectric multilayer film filter type, fiber brag grating type and arrayed waveguide grating (AWG) are put in practical use. Among them, AWG type optical multiplexer/demultiplexer comprising silica based glass waveguide is excellent with respect to mass productivity, cost and multi channeling, because it is manufactured by applying semiconductor process and optical fiber producing technique.
As shown in FIG. 1, this silica based glass waveguide is manufactured as follows. A core glass film (not shown in the figure) is formed on a silica glass substrate 61. A core waveguide 63 is formed by processing such as etching to the core glass film. After a plurality of optical waveguide are formed collectively on the silica glass substrate 61 by forming a clad 65 on the surface of the silica glass substrate 61 and the core waveguide 63, they are cut off for every waveguide.
However, in the conventional silica based glass waveguide 60 shown in FIG. 1, because slight unevenness of various kinds of parameters occurs in practical production process, designed optical characteristics (designed value) and actually obtainable optical characteristics (measured value) are often different slightly. Even thought by considering the core width variation which arise under manufacturing and the small sway of refraction index which arise at the core or at the clad film neighboring the core, the measured value is largely different from the designed value, and obtained each silica based glass waveguide are uneven respectively in optical characteristics, the yield rate is not satisfactory. Accordingly, there were problems in reliability, uniformity of products and yield rate under manufacturing.
Further, there was problem that connecting loss increases when an optical module was constituted by connecting an optical fiber (not shown in the figure) to at least one end of the core waveguide 63 of the silica based glass waveguide 60.